• 화약ㆍ발파
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• 제20권3호
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• pp.49-58
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• 2002

발파공법이 소개된 이후로 계속해서 많은 우수한 발파이론이 발표되어 왔다. 그러한 이론들의 저변에 있는 궁극적인 목표는 효율의 증가와 경제성이다. 이에 본 연구는 Air-Tubes 발파공법을 소개하고 터널에서 일반발파와 비교하여 그 발파효율을 검토해 보았다 연구의 배경이 되는 곳은 산청군 시천면 내대리와 하동관 묵계리를 연결하는 2차선 국도 터널 공사 현장이며 전체 총연장은 2Km이다. 진동측정방법은 하나의 발파진동을 4개의 측정기로 측정하여 데이터분석에 사용하였다. 일반발파와 Air-Tubes의 진동측정을 4개소에서 각각 6회씩 실시하여 총 24개씩의 진동측정 데이타를 얻었고 회귀분석을 실시하여 95% 신뢰도의 발파진동 추정식을 얻었다. 시험발파 및 진동측정에 이어 매 발파마다 광파측량을 실시하여 진행장을 구하였으며 사용한 장약량은 Air-Tubes 발파시 25% 정도 적게 사용하였고 발파진동이 23% 감소하였다. 발파당 굴진장 및 Smooth blasting 발파시의 벽면의 상태는 동일하고 파쇄석의 크기는 Air-Tubes 발파시 더 작게 나타난다.

• 설비공학논문집
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• 제11권6호
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• pp.740-748
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• 1999

This research was concerned with the enhancement of heat transfer by surfactant added to the aqueous solution of LiBr. Different vertical tubes were tested with and without an additive of normal octyl alcohol. The test tubes were a bare inner surface, groove inner surface, corrugated inner surface and spring inserted inner surface tubes. The additive concentration was about 0.08 mass%. The heat transfer coefficient was measured as a function of film Reynolds number in the range of 20~200. Experiments were tarried out at higher cooling water temperature of $35^{\circ}C$ to simulate an air cooling condition for several kinds of absorber testing tubes. The experimental results were compared with cases without surfactant. The enhancement of heat transfer by Marangoni convection effect which was generated by addition of the surfactant is observed in each test tube. Especially, it is clarified that the tube with an inserted spring has the highest enhancement effect.

• 소성∙가공
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• 제24권1호
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• pp.20-27
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• 2015

Hot tensile tests were conducted at different temperatures ranging from $20^{\circ}C$ to $550^{\circ}C$ to evaluate the mechanical properties of Al5052 seamless tubes. Such tubes can provide the technological foundation for complex forming using hot air bulging. Hot air bulging is one of the recently developed hydroforming techniques and it has some limitations in terms of cycle times. The benefits of hot air bulging are weight and cost savings through part consolidation and reduced post-forming processes such as welding and piercing. In order to extend the forming limits of Al lightweight material hot air bulging was investigated. A heated tube was placed in a heated die and sealed at the ends by sealing cylinders. The heated tube was subsequently expanded against the die cavity wall by internal pressure using air medium. The results of the current study show that axial feeding speed and air pressure have an effect on the formability of Al tubes during air bulging at elevated temperatures.

• 설비공학논문집
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• 제12권5호
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• pp.525-532
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• 2000

Evaporation heat transfer characteristics have been investigated experimentally when distilled water is sprayed on the outside wall of horizontal tubes in a evaporator. This problem is of particular interest in the design of evaporator of an absorption system. Hydrophilic surface treatment was employed to increase the wettability on copper tubes. The results indicate that evaporation heat transfer with hydrophilic tubes is shown to be 25-44% higher than that with bare tubes at evaporation pressure of 31.8 Torr(evaporation temperature$ 30^{\circ}C). Evaporation heat transfer rates of hydrophilic treatment tubes are improved substantially, comparing with those of conventional copper tubes in the wide range of operating parameters, such as water inlet temperatures, water mass flow rates and evaporation pressures.

• International Journal of Air-Conditioning and Refrigeration
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• 제12권4호
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• pp.198-205
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• 2004

An experimental study was carried on the characteristics of fluid flow and heat transfer in a fluidized bed shell-and-tube type heat exchanger with corrugated tubes. Seven different solid particles having same volume were circulated in the tubes. The effects of vari­ous parameters such as water flow rates, particle geometries and materials, and geometries of corrugated tubes on relative velocities and drag coefficients were investigated. The present work showed that the drag force coefficients of particles in the corrugated tubes were usually lower than those in the smooth tubes, meanwhile the relative velocities between particles and water in the corrugated tubes were little higher than those in the smooth tubes except the particles of glasses.

• 설비공학논문집
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• 제15권5호
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• pp.406-412
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• 2003

An experimental study was carried on the characteristics of fluid flow and heat transfer in a fluidized bed shell-and-tube type heat exchanger with corrugated tubes. Seven different solid particles having same volume were circulated in the tubes. The effects of various parameters such as water flow rates, particle geometries and materials, and geometries of corrugated tubes on relative velocities and drag coefficients were investigated. The present work showed that the drag force coefficients of particles in the corrugated tubes were usually lower than those in the smooth tubes, meanwhile the relative velocities between particles and water in the corrugated tubes were little higher than those in the smooth tubes except the glass.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권3호
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• pp.138-146
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• 2002

The phenomena of energy separation in vortex tubes was investigated experimentally to see the subsidiary effect of the conductivity of tube material and cooling conditions around the outer surface of the tube. The experiment was carried out with pyrex, stainless steel and copper tubes, and the heat transfer conditions of the tubes were with insulation, without in-sulation and water cooling modes respectively The results were obtained that the hot exit fluid temperature was highly affected by a change of conductivity of a tube when the outer surface was cooled by the water, while the working fluid through the tubes was air. How-ever, the cold exit temperature was little affected by the heat transfer modes on the outer surface of the vortex tube.

• 설비공학논문집
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• 제28권5호
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• pp.195-201
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• 2016

Enhanced tubes are widely used in air-conditioning and process industries. Structural tubes having three-dimensional roughness are well known to be able to significantly enhance pool boiling heat transfer of refrigerants. In this study, five structural enhanced tubes having different fin density, fin height, and fin gap width were tested using R-134a. Results showed that the heat transfer coefficient was increased with increased fin density. Within test range, the effect of fin height on pool boiling heat transfer coefficient was insignificant. The heat transfer coefficients of the optimum configuration (2047 fpm, 0.21 mm gap width) tube were lower than those of other commercial enhanced tubes. This might be due to the larger fin gap width of the present enhanced tube.

• 화약ㆍ발파
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• 제21권2호
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• pp.31-42
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• 2003

본 연구는 일반건설현장에서와는 달리 천공경이 $97mm{\Phi}$이상이고 천공장이 21M이상인 상태에서 발파작업이 진행되고 있는 석회석 광산에서 기존의 발파공법과 Air tubes를 이용한 발파공법을 비교하여 기존의 발파로 인한 상부 대괴를 감소시키고 폭약의 사용량을 줄이면서 진동 및 폭음을 최소화하여 보다 경제적인 작업수행을 하기 위해 연구하였다. 한편 에어층(Air deck)을 형성으로 인한 전색장의 길이 감소를 보완하기 위해 라바플러그(Rubber Plug)를 사용하므로 비석의 위험을 최소화 시키고 가스압이 암전체에 충분히 전달할 수 있도록 장치를 만들어 실험하였다. 그 결과 일반발파와 Air tubes를 이용한 발파방법을 비교하여 볼 때 Air tubes를 이용한 발파방법이 폭약을 약 15~30% 절감 할 수 있었으며, 또한 진동은 최대 50%정도의 감소와 폭음에서는 2~5dB 정도로 감소되었다.

• 대한기계학회논문집
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• 제1권1호
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• pp.17-25
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• 1977

관벽의 영향을 무시할 수 있는 요기내의 액체중을 상승하는 단일공기포의 상승속도, 형산, 경로를 명확히 하고 원주형관, 정방형관, 평행평판간의 액체중을 상승하는 단일기포의 상승속도에 미치는 관벽영향을 구하였다. 원주형관을 상승하는 공기포는 dimensionless plot로 실험치를 통 적으로 표현할 수가 있었으며 관벽영향을 받지않고 관중을 상승할 수 있는 공기포에 대한 최저의 관경을 결정할 수가 있었다.